U.S. Pat. No. 3,992,099 to Laughlin, incorporated herein by reference, discloses a source discriminator for measuring the angle of arrival and wavelength of beams of radiant energy. Such a system is useful in combat applications to provide information about the source of ranging laser beams and the like. The source discriminator described in the Laughlin patent includes first and second planar radiant energy detectors transversely oriented relative to one another to receive radiant energy. Each of the detectors produces an electrical output signal corresponding to radiant energy which impinges on the detector. The output signals are used to determine the angle of arrival and wavelength of the radiant energy impinging on the planar detectors. The detectors have an angular response approximated by the cosine function.
However, it has been found that the typical prior planar detectors used in the systems such as disclosed in the Lauglin U.S. Pat. No. 3,992,099 include a passivating overcoat on the surface of the detector. The passivating overcoat acts as an optical "transmission line" and thus by the electro-magnetic field theory, varies in its transmission of radiant energy as a function of the wavelength and polarization of the optical energy passing through it. The passivating overcoat thus tends to prevent a true cosine function angular response by the system. Variations caused by the passivating overcoat thus adversely affect the accuracy of results determined by prior detecting systems.
It is also been found that reflections from the detector mountings and reflections and shadowing by the surfaces of the detector housing and detector electrode post used with prior systems can adversely effect the accuracy of the prior systems.
The need has thus arisen for an improved radiant eergy discriminator which provides a true cosine angular response and which minimizes or eliminates the effects of the passivating overcoat of the planar detectors and reflections or shadowing by the detector mounting, housing and electrode post.